As electronic apparatuses have had small sizes, had a lot of functions, and be inexpensive, components included in the apparatuses are accordingly demanded to have small sizes, have long life time, and be inexpensive. Push-button switches of such components providing clear click feel upon operating are easily activated, hence being widely used in input units of the electronic apparatuses. The switches are accordingly demanded to have low, stable contact resistances and long operating life time.
A conventional push-button switch disclosed in Japanese Patent Laid-Open Publication No. 2002-334628 will be explained. FIG. 5 is a front cross sectional view of the conventional push-button switch. FIG. 6 is an exploded perspective view of the switch. A center stationary contact 2A and an outer stationary contact 3A provided by insert forming on the center and a periphery of a bottom of a case 1, respectively. The case 1 has a bottomed box-like shape and made of insulating resin material so that the contacts are electrically isolated from each other and have respective tops thereof. The center stationary contact 2A and an outer stationary contact 3A both made of metal material which have been firstly plated with nickel and then with silver. The center stationary contact 2A and the outer stationary contact 3A are connected to external terminals 2 and 3, respectively. A movable contact 4 made of stainless steel has a dome shape protruding upward.
The movable contact 4 includes a metal base, a nickel plated layer on the base, a palladium-nickel alloy plated layer on the nickel plated layer, and a gold-cobalt alloy plated layer on the palladium-nickel alloy plated layer. The plated layers face the stationary contact 2A. The movable contact 4 has an outer rim mounted on the outer stationary contact 3A in the case 1 while a center bottom 4A of the contact 4 is spaced by a predetermined distance from the center stationary contact 2A.
The center top of the movable contact 4 contacts a pressing portion 5A at a lowest part of a push button 5, an operation member, made of insulating resin. The push button 5 has an operating portion 5B at the upper part thereof projecting upward through a center opening 6A of a cover 6 for covering an upper opening of the case 1.
An operation of the conventional push-button switch will be explained.
When the operating portion 5b projecting upward through the center opening 6A of the cover 6 is pressed down, the push button 5 moves downward from a off-position shown in FIG. 5 and has the pressing portion 5A to apply a pressing force 5C to the top of the movable contact 4.
When the pressing force 5C exceeds a predetermined level, the top of the movable contact 4 is reversed to provide a click feel, and has the center bottom 4A contact the center stationary contact 2A in case 1. Then, the center stationary contact 2A is connected to the outer stationary contact 3A through the movable contact 4, thus having the push-button switch turned on.
Then, when the pressing force to the operating portion 5B of the push button 5 is released, the push-button switch is turned back to a off-position shown in FIG. 5 with an self-recovering action of the movable contact 4.
Electric signals corresponding to turning on and off of the switch are transmitted to a circuit in an electric apparatus (not shown) via the terminals 2 and 3 connected to the stationary contacts 2A and 3A, respectively.
In the conventional push-button switch, the lower surface of the movable contact 4 arranged to contact the stationary contacts 2A and 3A is coated with the nickel plated layer, the palladium-nickel alloy plated layer, and the gold-cobalt alloy plated layer in order to increase its operating life time and decrease a contact resistance Plating materials, such as palladium and gold, are expensive rare metals, thus preventing the push-button switch from being inexpensive.